Why don't you just do a compessability calc using bulk modulus with your dP. Is the temperature constant in this system??? Also what is the volume magnitude of this system???
If your sloping this piping then I assume it is drain piping requiring the use of gravity (i.e. non-pressurized piping). If your running the N-S and E-W piping in the same elevation then 45 deg elbows and "Y's" are better suited for these types of gravity assisted flows than 90 deg...
